vm: fix incorrect unlock error path in madvise_free_huge_pmd

Commit b8d3c4c3009d ("mm/huge_memory.c: don't split THP page when
MADV_FREE syscall is called") introduced this new function, but got the
error handling for when pmd_trans_huge_lock() fails wrong. In the
failure case, the lock has not been taken, and we should not unlock on
the way out.

Cc: Minchan Kim <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/huge_memory.c

···
 	int ret = 0;
 
 	if (!pmd_trans_huge_lock(pmd, vma, &ptl))
-		goto out;
+		goto out_unlocked;
 
 	orig_pmd = *pmd;
 	if (is_huge_zero_pmd(orig_pmd)) {